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<page xmlns="http://projectmallard.org/1.0/"
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type="topic" style="question"
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id="color-calibrationcharacterization">
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<link type="guide" xref="color#calibration"/>
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<desc>Calibration and characterization are different things entirely.</desc>
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<revision version="13.10" date="2013-09-07" status="review"/>
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<credit type="author">
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<name>Richard Hughes</name>
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<email>richard@hughsie.com</email>
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<include href="legal.xml" xmlns="http://www.w3.org/2001/XInclude"/>
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<title>What's the difference between calibration and characterization?</title>
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Many people are initially confused about the difference between calibration
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Calibration is the process of modifying the color behavior of a device.
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This is typically done using two mechanisms:
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<item><p>Changing controls or internal settings that it has</p></item>
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<item><p>Applying curves to its color channels</p></item>
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The idea of calibration is to put a device in a defined state with regard
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to its color response.
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Often this is used as a day to day means of maintaining reproducible behavior.
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Typically calibration will be stored in device or systems specific file
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formats that record the device settings or per-channel calibration curves.
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Characterization (or profiling) is <em>recording</em> the way
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a device reproduces or responds to color.
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Typically the result is stored in a device ICC profile.
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Such a profile does not in itself modify color in any way.
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It allows a system such as a CMM (Color Management Module) or a color aware
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application to modify color when combined with another device profile.
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Only by knowing the characteristics of two devices, can a way of
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transferring color from one device representation to another be achieved.
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Note that a characterization (profile) will only be valid for a device
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if it's in the same state of calibration as it was when it was
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In the case of display profiles there is some additional confusion because
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often the calibration information is stored in the profile for convenience.
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By convention it is stored in a tag called the <em>vcgt</em> tag.
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Although it is stored in the profile, none of the normal ICC based tools
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or applications are aware of it, or do anything with it.
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Similarly, typical display calibration tools and applications will not be
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aware of, or do anything with the ICC characterization (profile) information.
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